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Leaf miners

Leaf miners are larvae of flies, moths or sawflies that feed between the upper and lower leaf surfaces. Beet leaf miner blisters spinach and beet; allium leaf miner tunnels leeks and onions.

Pests
Pale winding leaf miner tunnels in a spinach leaf
Pale winding leaf miner tunnels in a spinach leaf

What it looks like

The damage is inside the leaf.

  • Pale, snaking lines that widen as the larva grows.
    Winding tunnels Pale, snaking lines that widen as the larva grows.
  • Brown, papery blisters on spinach and beet.
    Blotches Brown, papery blisters on spinach and beet.
  • Hold to the light to see the larva in the mine.
    Larva inside Hold to the light to see the larva in the mine.
  • Allium leaf miner leaves rows of white dots.
    Dotted stems Allium leaf miner leaves rows of white dots.

How to confirm it

Hold a leaf up to the light.

  1. See the larva

    A small grub inside a mine.

  2. Pattern

    Tunnels or blisters rather than spots.

  3. Timing

    Several generations through the season.

What to do

Squash and remove.

  1. Pinch the mines

    Squeeze the larva inside the leaf.

  2. Pick affected leaves

    Remove and bin mined leaves.

  3. Cover the crop

    Fine mesh keeps adult flies off.

  4. Harvest young

    Use leaves before damage builds.

Prevent it next time

  • Cover spinach and beet with mesh.
  • Rotate crops.
  • Clear weeds such as fat hen and dock.

What not to do

Do not bother spraying; the larvae are protected inside the leaf.

In the growing guides

Where the guides mention it, with plant-specific advice.

Sources

  1. Beet leaf miner, Royal Horticultural Society
  2. Leafminers on vegetables, University of Maryland Extension